snapspace

#!/bin/bash

function format_data ()
{
    local amount="$1"
    local suffixes=(" " "K" "M" "G" "T" "P" "E" "Z" "Y")
    local testnum="$amount"
    local divisor="1"
    local suffix=""
    for ((index = 0; index < ${#suffixes[@]}; ++index))
    do
        suffix="${suffixes[$index]}"
        testnum=`echo "$amount/($divisor)" | bc`
        if ((testnum < 1000))
        then
            break
        fi
        divisor="$divisor*1024"
    done
    local prespace="  "
    if ((testnum >= 100))
    then
        prespace=""
    else
        if ((testnum >= 10))
        then
            prespace=" "
        fi
    fi
    if [[ "$divisor" == "1" ]]
    then
        #don't use bc for non-fractional cases
        local displaydata="$amount   "
    else
        local displaydata=`echo "scale = 2; $amount/($divisor)" | bc -l`
        #we switch at 1000, not 1024, so check for having no digit before decimal point
        if [[ "$displaydata" == .* ]]
        then
            #because leading zero behavor is unspecified in bc
            displaydata=0"$displaydata"
        fi
    fi
    echo "$prespace$displaydata$suffix"
}

if (($# < 1))
then
    echo "usage: $0 <filesystem>"
    exit 1
fi
if [[ "$1" == *@* || "$1" == /* ]]
then
    echo "Snapshots and paths are not supported"
    echo "usage: $0 <filesystem>"
    exit 1
fi
#check that the filesystem is valid
if ! zfs get referenced "$1" > /dev/null
then
    #zfs will have printed an error message, so just exit
    exit 1
fi

echo " OLDREFS   UNIQUE  UNIQUE%   SNAPSHOT"
fullref=`zfs get -Hp referenced "$1" | awk '{print $3}'`
for snap in `zfs list -Hd 1 -t snapshot -o name "$1" | cut -f2- -d@`
do
    snapref=`zfs get -Hp referenced "$1"@"$snap" | awk '{print $3}'`
    snapwritten=`zfs get -Hp written@"$snap" "$1" | awk '{print $3}'`
    olddata=$((snapref + snapwritten - fullref))
    snapusedraw=`zfs get -Hp used "$1"@"$snap" | awk '{print $3}'`
    chars=`echo "$snap" | wc -m | awk '{print $1}'`
    if ((olddata > 0))
    then
        displaypercent=`echo "100*$snapusedraw/$olddata" | bc`
    else
        displaypercent=0
    fi
    if ((displaypercent < 100))
    then
        if ((displaypercent >= 10))
        then
            displaypercent=" $displaypercent"
        else
            displaypercent="  $displaypercent"
        fi
    fi
    echo "$(format_data "$olddata")   $(format_data "$snapusedraw")     $displaypercent%   $snap"
done